1. Field of the Invention
This invention relates to the field of polymer blends, or alloys, and in particular, this invention relates to blends of rubbery EVA copolymer and at least one other elastomer.
2. Description of the Prior Art
EVA copolymers constitute a well-known class of synthetic resins demonstrating a broad range of properties depending upon the relative quantities of copolymerized ethylene and vinyl acetate (and other ethylenic monomers which may be present) in the copolymer chain. Rubbery amorphous EVA gum stocks contain from about 40% to about 70% vinyl acetate by weight randomly distributed throughout the copolymer chain and, when crosslinked, for example, by a peroxide crosslinking agent, possess properties which make them especially useful as elastomers for rubber compounding, as base copolymers for adhesive formulations and as impact modifiers for polyvinyl chloride (PVC). Among the physical and chemical properties which make the rubbery EVA copolymers attractive for such applications are the following: heat aging resistance; oil and solvent resistance; low compression set; good low temperature performance; excellent weatherability and ozone resistance; resistance to natural light; transparent or white-to-black vulcanizates; high loadability; receptance to dielectric heating; and high dampening characteristics. Thus, the rubbery EVA copolymers are excellent candidates for such automotive applications as gaskets, seals and O-rings, wire insulation, radiator tubing and hose, bumper strips and auto body filler panels and are ideal for other demanding applications as well such as machinery mounts, weather stripping, washing machine hose, refrigerator gaskets, hydraulic hose, and the like.
It has been observed that, as synthesized by the high pressure process, the ethylene-vinyl acetate copolymers of this invention exhibit Mooney viscosities of only about 8-12, and although it has been found that these values can be approximately doubled by a suitable thermal working process (U.S. Pat. No. 3,968,091) the resulting worked gum stocks are still deficient in Mooney viscosity and green strength for many applications in the rubber industry. Accordingly, successful processing of EVA gum stocks of from about 40% to about 70% copolymerized vinyl acetate by weight requires that the Mooney viscosity and green strength be suitably increased, without, however, detracting to any appreciable extent from the desirable characteristics of rubbery EVA copolymers enumerated above.
While it is known that EVA copolymers and graft copolymers of EVA with another monomer such as vinyl chloride can be blended with one or more other elastomers (cf. U.S. Pat. Nos. 3,282,035; 3,322,858; 3,361,850; 3,361,852; 3,374,198; 3,422,055; 3,549,727; 3,600,461; 3,644,577; 3,718,711; 3,758,661; 3,808,047; 3,821,333; 3,941,859; and 4,102,855), heretofore there has been no recognition or appreciation that the Mooney viscosity and green strength of EVA gum stocks containing from about 40% to about 70% vinyl acetate by weight can be significantly increased upon the addition of certain elastomers as hereinafter described.